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Bathymetric Dynamic Digital Elevation Model Update

Bathymetric Dynamic Digital Elevation Model Update. NG-CHC Fall Retreat 25th to 26th October 2012. USM DDEM Team: Stephan O’Brien, Dave Dodd and Jerry Wiggert. MLW/MLLW CRM and NAVD88 CRM Comparison.

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Bathymetric Dynamic Digital Elevation Model Update

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  1. Bathymetric Dynamic Digital Elevation Model Update NG-CHC Fall Retreat 25th to 26th October 2012 USM DDEM Team: Stephan O’Brien, Dave Dodd and Jerry Wiggert

  2. MLW/MLLW CRM and NAVD88 CRM Comparison • An analysis was done between the 3 arc-second MLW CRM, 3 arc-second NAVD88 CRM and 1/3 arc-second NAVD88 Mobile DEM. • The CRM was translated from MLW to NAVD88 with VDatum. • The area analyzed was located in Mobile Bay and approximately 20 km2 .

  3. Difference: CRM NAVD88 – CRM MLLW_MLW Mean = -0.09 m St. Dev. = 0.002 m

  4. Difference: NAVD88 Mobile DEM – NAVD88 CRM Mean = -0.02 m St. Dev. = 0.07 m

  5. Development of DDEM using Generic Mapping Tools and VDatum • A set of methods was developed that use NOAA’s VDatum software and the Generic Mapping Tools (GMT) to produce the Dynamic Digital Elevation Model (DDEM) product. • As necessary, VDatum is used to translate the bathymetry from other datums to NAVD88. • The resampling of the CRM to finer resolution and the replacement of the CRM data with more recent bathymetry is done in GMT. • Statistical analysis of new data and existing CRM is also done in GMT. • One advantage of using these software tools is that they are freely available and accessible to all users.

  6. Development of DDEM using Generic Mapping Tools and VDatum • The current challenge is the smoothing along the edges of the bathymetric data sets replacing the existing CRM data. • The GMT command ‘grdblend’ will be used for this step. This command can combine partially overlapping grids and compute weighted average depths along the edges of the grid.

  7. Resample the 3 arc second Northern Gulf NAVD88 CRM (nCRM_3) to 1 arc second (nCRM_1) Translate the 3 arc second MLW/MLLW CRM (Volume 4) to NAVD88 using VDatum Update the 3 arc-second CRM with the 1 arc-second Northern Gulf DEM Update the nCRM_1 with Northern Gulf 1 arc second DEM Updated nCRM_1 to survey date 12/31/2001 Conduct a statistical analysis of the elevation differences between the nCRM_1 and the ingested Northern Gulf DEM

  8. Update the 1 arc-second CRM with the 1/3 arc-second NGDC DEMs Resample the nCRM_1 to 1/3 arc second (nCRM_1/3) Update the nCRM_1/3 elevations with currently available DEM products◉ Updated nCRM_1/3 to survey date 01/31/2009* Conduct a statistical analysis of the elevation differences between the nCRM_1/3 and the ingested DEMs ◉1) Southern Louisiana DEM; 2) New Orleans Louisiana DEM; 3) Biloxi Mississippi DEM; and 4) Mobile Alabama DEM * This is date of US ACE surveys. The most recent NOS Bathymetric Survey data used in developing these DEM products is from 2001-2003.

  9. Update the 1/3 arc-second CRM with most recent NOS surveys* Updated through 05/12/2010 Updated nCRM_1/3 Obtain NOS survey from NGDC repository. Translate from MLLW to NAVD88. Conduct a statistical analysis of the elevation differences between nCRM_1/3 and NOS survey. Update the nCRM_1/3 with translated NOS data. *Single-beam and multibeam surveys since 2001: Alabama (18); Mississippi (12); and Louisiana (51)

  10. VDatum Coverage Issues • The conversion of datums within VDatum is restricted by the extents of ‘Project Area’. • Not all the ‘Project Areas’ extend to the 200 m isobath. • One proposed solution is the use of VDatum to develop a MLW to NAVD88 separation model in the areas not covered by VDatum. • An additional issue is that off the coast of western Louisiana there is a gap between two VDatum project areas (~1.1 km).

  11. Vdatum Project Areas: Limits & 1.1 km Gap

  12. Availability of Bathymetric Data on DMS THREDDS Server • The NGDC DEMs are accessible on the web via the Department of Marine Science THREDDS server. • The available DEMs (all at NAVD88) are: • 1) Central Gulf of Mexico CRM (3 arc-second) • 2) Northern Gulf Coast DEM (1 arc-second ) • 3) Southern Louisiana DEM (1/3 arc-second ) • 4) New Orleans DEM (1/3 arc-second ) • 5) Mobile DEM (1/3 arc-second ) • 6) Biloxi DEM (1/3 arc second)

  13. Plans for Completed DDEM • The completed Bathymetric DDEM will be available as a web-accessible resource from the Department of Marine Science THREDDS server. • Software tools will be offered to users to facilitate OpenDAP data download of available DEM products, including updated nCRM_1/3. • Open source tools will be available for performing further nCRM_1/3 updates for users with access to personal or newer NOS bathymetric data.

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